This invention relates to an improvement in the operation of an oil sands hot water extraction plant.
In the extraction of oil from oil sands, oil bearing material is mined, usually by a bucket wheel excavator or dragline, and is transported for hot water extraction processing in which it is mixed with hot water such that the bitumen floats as a froth and the solid matter sinks, making it possible to skim off the froth for further separation and eventual refinement to finished products, and dump the solid matter.
Presently 87% by weight of bitumen and diluent naphtha are recovered from the oil sands by this hot water extraction process with a loss of 13% by weight being dumped with the solid matter. The disposing of the solid matter involves passing the solid matter together with accompanying hot water from the hot water extraction process out to tailings ponds. The hot water which is lost is at a temperature of approximately 185.degree.-195.degree. F. The loss of this hot water considerably reduces the overall plant thermodynamic efficiency as the heat loss must be made up when reheating cold water for the hot water extraction process.
In present commercial operations, the tailings containing solid matter, hot water, and hydrocarbons not removed by the hot water extraction process, are sluiced, after the process, into retaining areas which are often large ponds formed from dams or dykes built from the tailings. When the first pond has been filled, a second dam is built in the mined out area and this process of building dams and filling the ponds formed between the dams is continued until the reserve of mineable oil sands has been depleted. At this future time most of the area of the mined out acreage will be covered under almost a continuous pond consisting of water, oil emulsions, and clay fines gel. With the present method of tailings disposal, environmental authorities have determined that there has been and will continue to be pollution impacts on underground water streams, surrounding lakes and other fresh water bodies adjacent to the mining areas. Under the present tailings disposal little, if any, of the mined out land can be reclaimed and put to useable form since it will all be under the water, oil emulsion and unstable clay fines gel.
The basic method of recovery of oil from oil sands is disclosed in the following Canadian patents, however none of these patents are concerned with the efficiency of the system but only with general methods and apparatus for removing the oil. The disposal of the tailings and the deleterious environmental impact of the tailings on the land and surrounding water bodies were not considered of importance nor even recognized in these patents.
______________________________________ Patent No. Date Patentee ______________________________________ 448,231 May 4, 1948 Karl Adolf Clark 488,928 Dec. 16, 1952 Oil Sands Limited 493,081 May 26, 1953 Robert C. Fitzsimmons ______________________________________
Some of the major hitherto unresolved problems in the continued development of the oil sands are (1) to increase the recovery of bitumen from the sands and limit the loss of diluent use in a hot water extraction process, (2) to increase the thermodynamic efficiency of the overall process by recovery of hot water which is presently lost in the tailings ponds, (3) to reclaim the mined out areas, leaving them in a useable form, and (4) to eliminate the environmental impact of pollution of surrounding bodies of water by seepage of contaminated sluice pond water into fresh water bodies and underground streams, etc. It has been observed that large bitumen losses; considerably larger than indicated above; occur in commercial operation periodically due to plant malfunctions or upsets due to many causes. This invention acts as a safeguard back-up system to recover approximately 99% by weight of such high commercial bitumen losses whether continuous or discontinuous.